Vegetation dynamics and rainfall sensitivity of the Amazon PublicDeposited

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Descriptions

We show that the vegetation canopy of the Amazon rainforest is
highly sensitive to changes in precipitation patterns and that
reduction in rainfall since 2000 has diminished vegetation greenness
across large parts of Amazonia. Large-scale directional
declines in vegetation greenness may indicate decreases in carbon
uptake and substantial changes in the energy balance of the
Amazon. We use improved estimates of surface reflectance from
satellite data to show a close link between reductions in annual
precipitation, El Niño southern oscillation events, and photosynthetic
activity across tropical and subtropical Amazonia. We report
that, since the year 2000, precipitation has declined across 69% of
the tropical evergreen forest (5.4 million km²) and across 80% of
the subtropical grasslands (3.3 million km²). These reductions,
which coincided with a decline in terrestrial water storage, account
for about 55% of a satellite-observed widespread decline in the
normalized difference vegetation index (NDVI). During El Niño
events, NDVI was reduced about 16.6% across an area of up to
1.6 million km² compared with average conditions. Several global
circulation models suggest that a rise in equatorial sea surface temperature
and related displacement of the intertropical convergence
zone could lead to considerable drying of tropical forests in the
21st century. Our results provide evidence that persistent drying
could degrade Amazonian forest canopies, which would have cascading
effects on global carbon and climate dynamics.